Mineral fibers are used in a variety of products. The fibers can be used as reinforcements in products such as plastic matrices, reinforced paper and tape, and woven products. During the fiber forming and collecting process numerous fibers are bundled together as a stand. Several strands can be gathered together to form a roving used to reinforce a plastic matrix to provide structural support to products such as molded plastic products. The strands can also be woven to form a fabric, or can be collected in a random pattern as a fabric. The individual strands are formed from a collection of glass fibers, or can be comprised of fibers of other materials such as other mineral materials or organic polymer materials. A protective coating, or size, is applied to the fibers which allows them to move past each other without breaking when the fibers are collected to form a single strand.
Typically, continuous fibers, such as glass fibers, are mechanically pulled from a feeder of molten glass. The feeder has a bottom plate, or bushing, which has anywhere from 200 to 10,000 orifices. In the forming process, the strand is wound around a rotating drum, or collet, to form, or build, a package. The completed package consists of a single long strand. It is preferable that the package be wound in a manner that enables the strand to be easily unwound, or paid out. It has been found that a winding pattern consisting of a series of helical courses laid on the collet builds a package that can easily be paid out. Such a helical pattern prevents adjacent loops or courses of strand from fusing together should the strand be still wet from the application of the size material. The helical courses are wound around the collet as the package begins to build. Successive courses are laid on the outer surface of the package, continually increasing the package diameter, until the winding is completed and the package is removed from the collet.
A strand reciprocator guides the strand longitudinally back and forth across the outer surface of the package to lay each successive course. A known strand reciprocator that produces square edged, cylindrical packages includes a cam having a helical groove, a cam follower which is disposed within the groove and a strand guide attached to the cam follower. As the cam is rotated, the cam follower and strand guide move the strand longitudinally back and forth across the outer surface of the rotating package to lay each successive course.
FIGS. 1 and 2 show a conventional winder 5 with a strand supply 40. Fibers 43 are drawn from a plurality of orifices 42 in a bushing 41 and gathered into a strand 44 by a gathering member 45. Size is applied to coat the fibers by size applicator 46. The strand 44 is wound around a rotating collet 31 in a winding apparatus 30 to build a cylindrical package 20.
The winder 5 includes a strand reciprocator 10 that guides the strand 44 laterally back and forth across the package surface 21 to lay the strand in courses 24 on the package surface. The strand reciprocator 10 also includes a cylindrical cam 11 that has a helical groove 12 with curved ends 13 and is mounted for rotation about its axis 14. A cam follower 15 is disposed in the groove 12. The cam follower 15 extends outwardly from the cam and a strand guide 17 is attached to the end. A notch 18 is formed in the strand guide 17 to hold the strand 44. The cam follower 10 is restrained from rotating with the cam, so that rotation of the cam causes the cam follower to follow the helical groove, moving laterally across the package surface.
As shown schematically in FIGS. 3A and 3B, cam follower 15 includes a cam groove engaging portion, or "boat," 16 fitted into the cam groove 12. Upper and lower guides 51, 52 abut the upper and lower sides of the cam follower 15 to restrain it in the tangential directions as the cam 11 rotates in direction R. As the cam rotates, the side wall of cam groove 12 applies to the cam groove engaging portion 16 a normal force F.sub.N at its point of contact with the cam groove. Normal force F.sub.N has a longitudinal component F.sub.L and a tangential component F.sub.T. Longitudinal component F.sub.L urges the cam follower longitudinally to the right in FIG. 3A, providing the desired function of converting rotation of cam 12 into translation of cam follower 15.
The cam follower and the structures that it engages need to perform several other functions for the strand reciprocator to function properly. First, the tangential component F.sub.T of the normal force F.sub.N must be opposed to prevent the cam follower from moving downwardly. Second, cam follower 15 must be restrained radially to prevent it from moving radially out of cam groove 12. Third, the desired orientation of follower 15 with respect to the tangential direction R (for example, to maintain the notch 18 in the vertical orientation shown in FIG. 3A) needs to be established and maintained. Fourth, the cam follower 15 needs to be maintained in the appropriate orientation about the longitudinal axis L, to resist rotative moments about axis L (explained below). If cam groove 12 crosses itself (i.e. if more than a half-rotation of the cam is required for the cam follower to traverse the full length of the cam) the cam groove engaging portion 16 must be elongate, to be able to span the crossing (such as crossings C in FIG. 2). For high traverse speeds, desirable in strand winding, the cam follower should have a low mass to reduce the forces required to decelerate the cam follower to zero speed and to accelerate the follower to full speed at the ends of the traverse. Finally, for high speed operation, proper lubrication must be supplied to the cam follower's contact surfaces to reduce friction and wear.
FIGS. 3A and 3B schematically illustrate several of these functions. The tangential component F.sub.T of the normal force F.sub.N is opposed by force F.sub.T2 applied by lower guide 52 to the lower face of cam follower 15. Since the opposed forces F.sub.T and F.sub.T2 are radially offset, they generate a moment tending to rotate cam follower 15 clockwise in FIG. 3A. This moment is opposed by forces generated by engagement of the cam follower with other structures, such as by the force F.sub.M1 at the contact between the cam groove engaging portion 16 and the bottom of cam groove 12 and the opposed force F.sub.M2 generated at the contact between the cam follower 15 and the side of lower rail 52. The orientation of cam follower 15 with respect to the tangential direction R is maintained by engagement of the follower 15 with upper and lower rails 51, 52. The illustrated cam groove engagement portion 16 is cylindrical, and therefore could not be used with a multi-turn cam.
A known cam follower mechanism is illustrated schematically in FIGS. 4A and 4B. Cam follower 15 has an elongate cam groove engagement portion or boat 16, which permits the cam follower to traverse cam groove crossings. Since the cam follower is of one-piece construction, and the boat 16 is fixed with respect to the body of the cam follower, the follower 15 assumes the orientation of the cam groove 12. The cam follower 15 would therefore be oriented obliquely in the opposite direction to that shown in FIG. 4A when the follower 15 is an oppositely-angled portion of cam groove 12. The tangential component of the normal force on the cam follower is opposed by engagement of lower rail 52 with the lower oblique face 15a of the cam follower. Radially-outward movement of the cam follower is prevented by engagement of the arcuate outer surface of boat 16 with the arcuate inner faces of the rails 51, 52.
Another known cam follower mechanism is illustrated schematically in FIGS. 5A and 5B. Cam groove 12 is stepped, with an outer groove and a narrower, inner groove. Cam follower 15 has a cylindrical outer cam groove engagement portion 19a to engage the outer groove and an elongate, pivotally-mounted inner cam groove engagement portion 19b to engage the inner groove and span crossings of the grooves. Cam follower 15 includes upper and lower channels 53, 54 that engage rails 51, 52. The engagement of the rails and channels fixes the orientation of the cam follower in the radial direction, about the longitudinal axis, and with respect to the tangential direction.
Although the known cam follower mechanisms described above work well, they suffer from some shortcomings. The first cam follower mechanism does not maintain a fixed orientation of the follower, and provides relatively small bearing surfaces, which are difficult to lubricate effectively. The second cam follower is more complex, with a separate, movable cam groove engagement portion, and has a relatively high mass. Further, the engagement of the channels and rails is difficult to lubricate.